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| author | Masahiro Yamada <masahiroy@kernel.org> | 2023-06-11 17:50:57 +0200 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2023-06-22 14:21:06 +0200 |
| commit | 5e9e95cc9148b82074a5eae283e63bce3f1aacfe (patch) | |
| tree | 72072798944c4a0ffcf2f294b8c264cbd7f60b05 /scripts/remove-stale-files | |
| parent | modpost: use null string instead of NULL pointer for default namespace (diff) | |
| download | linux-5e9e95cc9148b82074a5eae283e63bce3f1aacfe.tar.xz linux-5e9e95cc9148b82074a5eae283e63bce3f1aacfe.zip | |
kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without recursion
When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an
EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
second traverse, where some source files are recompiled with their
EXPORT_SYMBOL() tuned into a no-op.
Linus stated negative opinions about this slowness in commits:
- 5cf0fd591f2e ("Kbuild: disable TRIM_UNUSED_KSYMS option")
- a555bdd0c58c ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding")
We can do this better now. The final data structures of EXPORT_SYMBOL
are generated by the modpost stage, so modpost can selectively emit
KSYMTAB entries that are really used by modules.
Commit f73edc8951b2 ("kbuild: unify two modpost invocations") is another
ground-work to do this in a one-pass algorithm. With the list of modules,
modpost sets sym->used if it is used by a module. modpost emits KSYMTAB
only for symbols with sym->used==true.
BTW, Nicolas explained why the trimming was implemented with recursion:
https://lore.kernel.org/all/2o2rpn97-79nq-p7s2-nq5-8p83391473r@syhkavp.arg/
Actually, we never achieved that level of optimization where the chain
reaction of trimming comes into play because:
- CONFIG_LTO_CLANG cannot remove any unused symbols
- CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is enabled only for vmlinux,
but not modules
If deeper trimming is required, we need to revisit this, but I guess
that is unlikely to happen.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to '')
| -rwxr-xr-x | scripts/remove-stale-files | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/scripts/remove-stale-files b/scripts/remove-stale-files index 7f432900671a..f3659ea0335b 100755 --- a/scripts/remove-stale-files +++ b/scripts/remove-stale-files @@ -33,3 +33,7 @@ rm -f rust/target.json rm -f scripts/bin2c rm -f .scmversion + +rm -rf include/ksym + +find . -name '*.usyms' | xargs rm -f |